FAQs on the VSV-ZEBOV vaccine against Ebola virus

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Professor Claire-Anne SiegristProfessor
Claire-Anne Siegrist
Head of Vaccinology Center

22. How and by whom is this vaccine manufactured?

The VSV-ZEBOV vaccine was developed by Canadian scientists and produced by IDT Biologika, a German company, under a licensing agreement with NewLink Genetics (USA). Its manufacturing process has met the highest standards for pharmaceuticals (GMP).
Also see diagram: "VSV-ZEBOV vaccine against Ebola"

23. If the vaccine is "live", why is it not dangerous?

The VSV-ZEBOV vaccine is produced using a virus which is not considered dangerous for humans – the vesicular stomatitis virus (VSV) – which was modified to display the surface protein found on the Ebola virus. These proteins should trigger an immune response in vaccinated individuals with no risk of acquiring Ebola virus disease.
The VSV virus is easily eliminated by the human body and causes, in the worst case, symptoms comparable to a mild flu lasting 2 to 4 days. In addition, the VSV has been attenuated to further reduce these symptoms. But since VSV-ZEBOV is a “new” virus, it could trigger slightly different reactions.
"Live" but attenuated vaccines are usually more effective than vaccines solely based on viral proteins. They are already widely used, for example against mumps and measles. Their main advantage is to trigger a stronger immune response: they generally do not require a subsequent booster vaccination.

The use of the VSV for immunization has other advantages:

• Being an RNA virus, its genetic material cannot insert itself into human DNA.
• As the VSV does not usually infect humans, there is no risk of the virus contained in the vaccine recombining with human strains of the same virus.
• Very few people have been exposed to this virus: therefore, basic immunity in the human population against VSV is very low, which should make it more effective for vaccination.


24. Has the vesicular stomatitis virus (VSV) already been used for other vaccines or therapeutic treatments?

The VSV has also been used to develop experimental vaccines against HIV. Tests on mice and monkeys using modified VSVs have given excellent results for treating melanomas, lung cancer, colorectal cancer, and brain tumours.

25. Is this vaccine protected by  "Intellectual Property Rights" which prevent other laboratories from producing it?

The Canadian government still owns the intellectual property rights associated with the VSV-ZEBOV vaccine. In 2010, it licensed the production and marketing to NewLink Genetics (USA). Under the terms of an agreement signed in November 2014, Merck was granted these rights for production and marketing.

26. What are the odds for this vaccine being effective?

For the vaccine to be effective, it must stimulate the body to produce antibodies that neutralize the Ebola virus. VSV-ZEBOV vaccine should induce a good antibody response, because it multiplies for a few days in the body before being eliminated. If it triggers an immune response against the Ebola virus that is as strong as what has been observed in monkeys, a single injection could provide a very high and lasting level of protection.

Prof. Bernard Hirschel, President of the Cantonal Commission of Research Ethics (Geneva) and HIV specialist: "Between HIV and the Ebola virus, there is a big difference. The HIV-infected person develops an immune response with antibody production, but cannot defeat the disease. With Ebola, the person who survives the disease becomes immunized against the virus. So there is a great hope that vaccines will be effective."

27. Could the Ebola virus mutate - like the flu virus - and therefore make the vaccine ineffective?

That cannot be excluded, but the Ebola virus does not mutate as quickly as the flu virus or HIV. Therefore, major changes in the Ebola-Zaire virus (the strain causing the current epidemic) which would render the vaccine ineffective are unlikely – even if we cannot totally exclude this eventuality. The mode of transmission and mortality rates observed for the current virus are in fact very similar to those of the first Ebola virus identified in 1976 in Zaire (now Democratic Republic of Congo).

28. How long after vaccination would the protection become effective?

If the VSV-ZEBOV vaccine works as well in humans as it does in monkeys, partial protection should be achieved after 2 weeks, and a good level of protection after 4 weeks. But to date, we still do not know whether the vaccine will enable the production of antibodies, and whether these antibodies can neutralize the envelope of the Ebola virus which causes the disease.

29. How long is the vaccine’s protective effect likely to last?

If the VSV-ZEBOV vaccine works as well on humans as it does on monkeys, it will achieve a long-lasting protection. As in other “live” vaccines, such as those against measles or yellow fever, it may be possible that a single injection – of a suitable dose, to be determined – would be sufficient to ensure sustained protection for life.

30. Will it be possible to vaccinate children? And what about animals, including those that could potentially transmit the virus to humans?

The question of children, pregnant women and older people is crucial, because they pay a heavy toll to the Ebola virus disease. But the first vaccination trials with VSV-ZEBOV will be limited to people aged between 18 and 65. Future studies will determine whether this vaccine may also be safe and effective for children, older people, etc.

For pregnant women, caution is the rule when it comes to live vaccines which are able to multiply, such as VSV-ZEBOV. Other vaccine candidates which do not replicate, such as the one currently tested at the CHUV in Lausanne, might be better candidates for them.

The vaccination of animals in order to prevent transmission to humans is highly unlikely, because free-living bats are probably the primary reservoir of the virus.

31. If the vaccine works well, is there any hope that we will be able to use it on people who have already been contracted Ebola virus disease?

Maybe. Preliminary post-exposure testing in monkeys showed possible efficacy, but only if the vaccine is administered a few hours after infection. Further studies will be needed before any strong conclusions can be drawn about post-exposure prophylaxis. Vaccination is one of the experimental treatments which can be proposed to persons who have been exposed to the virus.


Dernière mise à jour : 29/01/2019